1. Field of the Invention:
The present invention relates to a flame- and smoke-resistant polyurethane foam and a method for producing said polyurethane foam.
2. Description of the Prior Art:
It is well known to produce polyurethane foams by a combination of a polyol, a polyisocyanate, water and/or other blowing agent, a catalyst and a surfactant. A variety of foams, such as flexible, semi-rigid and rigid polyurethane foams, can be obtained depending upon the number of functional groups, molecular weight and skeleton structure of the components to be used. These polyurethane foams are widely used as sheet and cushioning materials for furnitures, vehicles, aircrafts and ships and as a material for cloths and buildings. Although polyurethane foams are used in various fields due to the characteristic property, the foams have a serious drawback in the inflammability. In order that the polyurethane foams are fully suitable for these uses, the use of polyurethane foams having flame resistance has recently been demanded. Moreover, the legal regulation of the use of flame-resistant polyurethane foams becomes more strictly year after year, and this tendency is noticeable in the polyurethane foams for motorcars, railway vehicles and aircrafts.
Heretofore, various attempts have been made with respect to the method for providing the flame resistance to polyurethane foams. However, although conventional methods, that is, the use of addition type flame retardants, such as phosphorus-containing compound, halogen- and phosphorus-containing compound, antimony oxide and other metal oxides, or the use of reaction type flame retardants can provide a certain degree of flame resistance for the polyurethane foams, but the polyurethane foams, which have been judged as non-burn by the burning test (ASTM-D-1692-59T), are few. Moreover, in these processes, a relatively large amount of the flame retardant is required, and therefore these processes are not preferable in view of economy. Further, the addition type flame retardants decrease in the effect with the lapse of time and further act as a plasticizer, and therefore, the use of the addition type flame retardant has an adverse influence upon the general physical properties of the resulting foam. While, the use of the reaction type flame retardant affects adversely the foaming stability and general physical properties of the resulting foam and causes scorch and other unfavorable phenomena during the production of the foam, and therefore, it is difficult to use a large amount of the reaction type flame retardant, and the effect of the use thereof is low. Moreover, the flame-resistant foam obtained by the use of these flame retardants is apt to be larger in the emission of smoke upon burning than the polyurethane foam containing no flame retardant, and threre is a serious problem in the use of flame-resistant foam containing these flame retardants in view of the smoke emission. Namely, in the conventional process, it has been difficult to provide both the properties of high flame resistance and smoke resistance for polyurethane foam.